Find Marshalls telephone number and ring them up on Monday morning. I've only been growing potatoes for a few years, but I've never had any do that. I'd definately be ringing up the supplier if they did!

I would bet the larger of MY two potatoes that frost has got to them.
The same has happened to some i had chitting at the allotment shed they are also wet to the touch bleeding a black liquid and soft.
The sprouts have also blackened and turned mushy.
I have about 4 varieties from different suppliers chitting in the shed and it affected them all thus ruling out a bad individual batch.
Minty